1. Field of the Invention
The invention generally relates to devices having stacked modules, and to corresponding stackable modules and operation methods, and in particular to the assignment of resources in such devices.
2. Description of the Related Art
Stacked module devices exist where a number of compatible modules are stacked onto a host board. The modules may be PCBs (Printed Circuit Boards) which are placed one on top of the other, but the modules may also be single chips, or larger groups of components. In any case, a module has a bottom connector to connect to the neighboring module located below the respective module, and a top connector to connect to the next upper module.
Such stacked module devices often receive resource related signals from the very bottom. Resource signals may in this context be, for instance, clock signals, chip select signals, or address signals. The lowest module receives the signals and feeds the signals through to the next module which is located upwards. This module does substantially the same, i.e., it forwards the received signals to the next upper module. By this scheme, all of the modules are enabled to access the resources.
FIG. 1 depicts a conventional stacked module device having four modules 100-130. In the example of FIG. 1, six resource related input signals are fed through the modules, thereby forming a signal bus. As apparent from FIG. 1, each module may use one or more of the resources, for instance to synchronize to a specific clock, to use specific chip select signals, or to be addressable at a given address, or access a separate memory (not shown) at a given address.
However, there may be a resource conflict if two or more modules 100-130 access the same resources. For that reason, each module 100-130 requires an individual resource selection device 140-170 to assign resources to the respective stack position. The resource selection devices 140-170 may be preconfigured, or there may be an extra signalling bus connecting the resource selection devices to each other, allowing the devices 140-170 to communicate to each other in order to avoid a conflict.
However, the necessity to provide selection devices on every stack position is often found to be detrimental since this involves additional hardware efforts and reduces flexibility. Moreover, adding a further module to the stack may require a reconfiguration of the existing modules in the stack. This may further reduce the reliability of the entire system.